1. Field of the Invention
The present invention relates to a high frequency module on which a component is mounted on an upper surface of a multilayer substrate. More specifically, the present invention relates to a technique of manufacturing a high frequency module at reduced cost while preventing electromagnetic coupling between an in-plane conductor that is provided in the multilayer substrate and the component and reducing the size of the high frequency module.
2. Description of the Related Art
With size reduction of a communication terminal device such as a cellular phone, a high frequency module that is arranged therein is required to be reduced in size. In order to achieve this, a multilayer substrate capable of establishing three-dimensional wiring has been widely used for a circuit substrate of the high frequency module. For example, a high frequency module 100 as described in Japanese Patent Application Laid-open No. 2008-244179 (see, for example, paragraph 0022, FIG. 1, and the like) includes a multilayer substrate 101 and a semiconductor element 102 as illustrated in FIG. 7. The multilayer substrate 101 is formed by laminating a plurality of insulating layers. The semiconductor element 102 is mounted on the upper surface of the multilayer substrate 101. Further, a ground electrode 103 for grounding is provided in the multilayer substrate 101 on a portion under the semiconductor element 102.
An area of the main surface of the multilayer substrate 101 is restricted in order to reduce the high frequency module 100 in size. Under this condition, when wiring paths that are connected to respective terminals of the semiconductor element 102 are tried to be formed in the multilayer substrate 101, there is no choice but to form some wiring paths that are connected to predetermined signal terminals so as to pass through portions under the ground electrode 103 in some cases. For coping with this, in the high frequency module 100, openings are provided on portions of the ground electrode 103 at positions just under the predetermined signal terminals of the semiconductor element 102 and through-holes 104 passing through the openings are provided on the multilayer substrate 101. Further, the predetermined signal terminals are connected to wiring electrodes 105 and 106 formed at the lower side of the ground electrode 103 through the through-holes 104. With this, the wiring paths that are connected to the predetermined signal terminals are led out to outer side portions of the semiconductor element 102 through the portions under the ground electrode 103.
The existing high frequency module 100 has the configuration in which some wiring paths that are connected to the predetermined signal terminals of the semiconductor element 102 are provided on the portions under the ground electrode 103 by providing the openings on the ground electrode 103 and forming the through-holes 104 passing through the openings. The configuration, however, increases the manufacturing cost of the high frequency module 100. In order to manufacture the high frequency module 100 at reduced cost, it is considered that the wiring electrodes 105 and 106 at the lower side of the ground electrode 103 are provided at the upper layer side of the ground electrode 103 and are connected to the predetermined signal terminals through via conductors or the like. However, when the wiring electrodes 105 and 106 pass through portions just under the semiconductor element 102, there is a risk that electromagnetic coupling is generated between the semiconductor element 102 and the wiring electrodes 105 and 106 and high frequency characteristics are deteriorated. For this reason, it is difficult to use the above-mentioned configuration.